This invention pertains to urea-aldehyde dispersions useful as fertilizers which have long lasting nitrogen release characteristics coupled with low plant damaging properties, to processes for preparing such dispersions and to their application. More particularly, it relates to dispersions formed during polymerization reactions of urea and formaldehyde when modified by the use of small amounts of a higher aldehyde containing from 2 to 4 carbon atoms as cross-link inhibitors or chain stoppers to prevent the setting-up or hardening of the dispersions upon aging. Settling is minimized by the addition of thickener-suspending agents and the solids made dispersible on plants by the addition of surfactants.
Urea formaldehyde condensation polymers have been used extensively for many years alone or in conjunction with fillers or sheets to make solid or laminated products. Scrap material from such products was used as a cheap source of nitrogen fertilizer, but proved unrealiable and uncontrollable. Yee and Love, Proc. Soil Sci. Soc. Am., 11, 389-92 (1946) and Clark, Yee and Love, Ind. Eng. Chem., 40, 1178-83 (1948) demonstrated that the control of the rate of useful nitrogen release from urea formaldehyde polymers was a function of urea/formaldehyde ratio, molecular weight, cold and hot water insolubility and other factors.
It is desirable to provide fertilizers which release nitrogen at rates which enhance the growing of plant life and in particular, turf, without damaging the plant root systems or the foliage by the excessively rapid uptake of nitrogen, nor starving the plants because of a severely low rate of nitrogen release.
Generally, urea formaldehyde fertilizers in solid form have found widespread use but are difficult to apply uniformly. The rate with which nitrogen is made available to the plants is a function of the composition of a urea aldehyde fertilizer. Soluble, unreacted urea releases nitrogen rapidly; soluble, low molecular weight reaction products of urea and aldehydes release nitrogen less rapidly; cold water insoluble nitrogen (CWIN) in the polymeric products is slowly released; and hot water insoluble nitrogen (HWIN) in the polymeric products is released only over long periods of time. The methods for determination of the water insoluble nitrogen (WIN) and the proportion of CWIN and HWIN are given in the Official Methods of Analysis of the Association of Official Agricultural Chemists, 11th Ed., 1970. The composition which is preferred varies with the application. For example, commercial lawn applicators prefer complete nitrogen release in sixty to ninety days whereas golf course operators prefer longer release periods, requiring products with high WIN.
Attempts to produce fertilizers which release nitrogen at some controllable rate have taken several forms. For example, U.S. Pat. No. 3,441,539 to Helmut Karl Schafer et al., reported that slow nitrogen release granulated fertilizers are produced by co-condensation reactions of urea, a saturated aldehyde having 3-4 carbon atoms and formaldehydes wherein the saturated aldehyde is present in greater molar concentration than formaldehyde. An improvement in the handling characteristics of these solid products is claimed in U.S. Pat. No. 3,326,665, by Helmut Karl Schafer, et al., by the addition of certain swellable substances such as carboxymethyl cellulose, polyacrylamide, etc to the reaction mixture in the absence of solvent.
Another approach to the problem is exemplified by U.S. Pat. No. 3,054,669, to Johann Jung, et al., which shows that crotylidene diurea alone or in admixture with other nitrogenous fertilizers and inert materials can be applied to the soil as slow-acting nitrogenous fertilizers.
Many other patents describing the preparation and use of urea-aldehyde reaction products for providing slow acting fertilizers will be familiar to those skilled in the art.
However, for ease and uniformity of application to fill the specific needs of turf areas such as golf courses, nurseries, institutional and home lawns, especially those serviced by commercial lawn care operators, it is economically desirable to provide nitrogen at growth promoting levels for relatively long periods by means of application of liquid fertilizers.
The present methods of preparing liquid fertilizers are those which involve the milling of solid urea-formaldehyde or other polymeric sources of nitrogen, blending the pulverized materials with additives to facilitate wetting and the formation of stable dispersions in aqueous systems and pumping the resulting dispersions through conventional spray nozzle applicator equipment. Unfortunately, such techniques are often unsatisfactory because of the difficulty in achieving particle size distributions which, on the one hand, do not contain substantial amounts of fines which blow away in the wind or, on the other, coarse particles which clog the spray nozzles or, even worse, settle into non-dispersible aggregates in the spray tanks.
The preparation of liquid fertilizers of urea formaldehyde polymers is summarized in U.S. Pat. No. 4,033,745 to William Percy Moore, entitled "Non-Burning Storable Liquid Fertilizer." The Moore patent provides a suspension of urea formaldehyde polymers which is stabilized by the use of alcohol and sugar additives.
The present invention provides stable, aqueous dispersions of urea-aldehyde polymers useful as sprayable liquid fertilizers in the growing of crops, particularly lawn crops, which are storable for relatively long periods of time and reduce the danger of clogging the spray equipment. After application to the plants, the urea-aldehyde contained in the dispersion releases nitrogen for use by plants at rates desired by the user without burning the plants and without frequent application.